The present invention relates to video monitoring systems which employ one or more monitor television screens and one or more television cameras.
There is an increasing demand for video monitoring systems which can be employed for security systems in houses, offices, warehouses, government, buildings and the like to prevent theft, unauthorized entry, and so forth.
Almost all video monitoring systems are expensive and use large television cameras and television monitors. Therefore, relatively large constructions are required to support them.
A video monitoring system kit which can easily be installed in such locations as houses has been proposed in a Japanese Patent Application First Publication (Tokkai) sho No. 61-269586 published on Nov. 28, 1986. The video monitoring system kit in the above-identified Japanese Patent Application document includes a small television camera, a small television monitor, and a connector cable. These components are packaged in such a way that users can easily install the system components at the required places. Usually with this type of system, the television camera is focused on the area to be monitored and connected to the television monitor via the cable so that video images may be transmitted to the latter.
The camera operates on a low DC voltage that is supplied to it from an AC-DC converter in the television monitor i.e., an AC adaptor connected to a receptacle of a commercial AC power supply. If it is desirable to view the image produced by the camera by means of a second video monitor installed, for example, at a location other than the location of the first television monitor, the video signal input of the second television monitor is connected to the video signal output of the first television monitor.
There is a problem with the system described above in that, in order to view an image output by the camera on the second television monitor, the power supplies of both the first and second television monitors must be turned on because the camera receives its power from the AC-DC converter of the first television monitor and also the second television monitor is dependent on the first video monitor to output a signal from its video signal output. Furthermore, if a third television monitor is to be employed, the power supplies of all three television monitors must be turned on in order to view the image output from the camera on it since the video signal input of the third television monitor must be connected to the video signal output of the second television monitor which in turn is similarly connected to the first television monitor which is connected directly to the camera. Still another disadvantage of this arrangement is that the image output by the camera deteriorates at each stage in the series so that as more television monitors are added to the system, the quality of the image seen on the last monitor in series accordingly becomes worse.
These problems may be solved by means of a signal distributing device in which a plurality of amplifiers are built and a DC voltage supply (AC adaptor) is connected to all amplifiers. The signal distributing device supplies the video camera with the low DC voltage and receives therefrom a video signal. The inputs of the amplifiers are connected in parallel at input of the signal distributing device for receiving the signal output from the camera and the outputs thereof are connected to a plurality of output jacks through which a video signal can be output to a plurality of television monitors. In this way, each of the television monitors receives an equally clear signal. However, in this type of system, the number of television monitors is limited by the number of output jacks on the signal distributing device.
In addition, a high power AC adaptor i.e., an (AC-DC converter) needs to be connected to the distributing device with power supplies of all amplifiers taken into account.